This invention relates generally to aircraft control and, more specifically, to control of steerable aircraft landing gear.
Steer-by-wire systems can greatly simplify design and sometimes, operation of moving vehicles. Designing a mechanically-steered vehicle typically involves positioning operator controls close enough to steering devices to permit the operator controls to engage turnable wheels or steerable nose gear. To take the example of an automobile, a conventional rack and pinion steering mechanism involves placing the steering column such that one end is directly coupled to the front wheels and an opposite end is positioned in front of a driver""s seat. Once the steering column is in place, other drive train and supporting components are positioned around the steering column under the hood, and the dashboard and other operator controls are positioned around the steering column in the passenger compartment Therefore, significant design aspects of the automobile are dictated by a functionally-dictated placement of the steering controls.
Similarly, placement of mechanical operator controls for a nose gear steering mechanism for an aircraft also dictates aspects of the design of the aircraft and flight deck. A tiller serving as an operator control for the nose gear steering mechanism is placed to enable practical access to nose gear steering hydraulics. Design limitations are even more restrictive when considering the duplicate operator controls which commonly are used in aircraft flight deck. For example, providing two tillers to control a nose gear steering mechanism not only involves placing a first tiller with a practical mechanical linkage to the nose gear steering mechanism, but also involves placing a second tiller where it can be mechanically linked with the nose gear steering system or with the first tiller. Although the second tiller does not have to be coupled directly with the nose gear steering system, having a mechanical linkage between the two tillers may limit how other devices can be installed in the cockpit around and between the tillers.
Using steer-by-wire controls to operate the nose gear steering system can alleviate some of these placement and design concerns. In a steer-by-wire system, a mechanical linkage between operator controls and the steering device is replaced with an electrical system, thereby obviating the need for a direct mechanical linkage between the operator controls and the steering device. More specifically, the operator controls are linked with an electrical transducer that reads the operator input and generates an electrical signal representative of the operator input. The representative electrical signal is communicated to a corresponding electrical driver coupled with the steering mechanism, and the electrical driver directs the steering mechanism in a direction corresponding to the operator input. Accordingly, the steering mechanism is controlled by the operator as he or she might control it using a mechanical linkage but without there having to be mechanical linkages between the operator controls and the steering mechanism.
However, steer-by-wire systems present concerns not shared in systems employing mechanical linkages. For example, steer-by-wire systems do not naturally present feedback to an operator in the way that mechanically-linked systems do. Once more considering the example of an automobile, a mechanical linkage presents steering resistance to the operator in proportion to the resistance caused by the sharpness of the turn. Also, while a mechanically-linked steering wheel naturally spins back to normal as the steered wheels return to a straight-ahead position, there is no such natural response imparted to operator controls in a steer-by-wire system. Returning the steer-by-wire controls to an original position involves an application of an impetus to return the controls to such a neutral position.
The example of nose-wheel steering in an aircraft having duplicate controls presents an additional concern. In a steer-by-wire system, it is possible that the pilot and co-pilot might both be trying to control the nose-wheel steering system, and the force being applied by one operator might not be communicated to the other operator through the controls. Accordingly, the operators conceivably might be applying contradictory inputs to the control devices without the other operator knowing of it, defeating both their purposes. In an extreme case, both operators might apply equal force to the control devices thereby resulting in an excessive net steering input. Also, if such steering problems occur, and one operator suddenly releases his or her control, the response of the steering system to the unopposed or unsupported force on the control still being maintained could result in under-steering or over-steering.
Thus, there is an unmet need in the art for a steer-by-wire system that provides feedback through the operator controls reflecting a status of the steering mechanism. There also is an unmet need for a steer-by-wire system for providing non-mechanical linking between multiple operator controls such that each of the operators can be apprised of the effect on the steering mechanism resulting from other operators"" actions.
The present invention provides a steer-by-wire steering system and method providing feedback to one or more operator controls indicative of a position of the steering mechanism, and an aircraft using the system. Embodiments of the present invention use a tiller module in which a tiller is coupled with a moveable base. The tiller is movably secured to the base so as to be moveable within a range of a few degrees relative to the base or is rigidly secured to the base. Force applied to the tiller by an operator is determined by measuring the relative displacement of the tiller relative to the moveable base or by measuring strain in the tiller relative to the base. A differential signal is measured and applied to a tiller controller which generates a steering signal to the steering mechanism. A steering mechanism monitoring position device communicates a position signal back to the tiller module causing the moveable base to be moved to reflect a position of the steering mechanism. When multiple tiller modules are used, differential signals measured at each tiller module are summed and provided to the tiller controller. A steering mechanism monitoring position device communicates the position signal back to each of the tiller modules causing the moveable bases to be moved such that each tiller reflects a position of the steering mechanism.
More particularly, embodiments of the present invention provide a system and a method for generating a signal to control a steering mechanism. A tiller module includes a moveable tiller base configured to moveably respond to a steering signal. The tiller module also includes a tiller coupling configured to couple the tiller with the moveable tiller base and further configured to generate a tiller differential signal indicative of a steering force applied to the tiller relative to a position of the moveable tiller base. A tiller controller is configured to receive the tiller differential signal and a steering mechanism position signal. The tiller controller is further configured to generate the steering signal to direct a steering mechanism to conform with the steering force and to direct the moveable tiller base to a feedback position representative of a current position of the steering mechanism.
In accordance with further aspects of the present invention, the tiller coupling includes a centering spring mechanism configured to receive the tiller and allow movement of the tiller relative to the moveable tiller base within a predetermined displacement range. The tiller input coupling includes a tiller position transducer configured to measure a displacement of the tiller and generate the tiller differential signal. Alternatively, the tiller input coupling also includes a force transducer configured to generate the filler differential signal as a function of a strain resulting from the steering force applied to the tiller relative to the position of the moveable tiller base. In embodiments of the present invention, the tiller includes a rotatable handle and the moveable tiller base includes a rotatable base moveable by a motor receiving the steering signal.
In accordance with further aspects of the present invention, the tiller controller converts the tiller differential signal into the steering signal such that the moveable tiller base of each tiller module is moved to cause the tiller to be aligned to a position representative of the steering mechanism position signal. The tiller controller integrates the tiller differential signal such that a rate of change of the steering signal is proportional to a magnitude of the steering force. The tiller controller further includes a steering signal decay function such that a reduction in the tiller differential signal causes a resulting reduction in the steering signal causing the steering mechanism and the moveable tiller base to return toward a neutral position. The tiller controller further includes a position limiter restricting the tiller such that the feedback position of the tiller is representative of the current position of the steering mechanism.
In accordance with still further aspects of the present invention, redundant components are used to allow the steering system to continue to operate even when some components have failed. Redundant secondary components suitably are configured to perform the same functions as primary components. The secondary components can quickly replace the function of failed primary components allowing the steer-by-wire system to continue to function. In addition, a steering system using multiple tiller modules provides fault tolerance in that, should one tiller module fail, steering can still be controlled using the other tiller modules.
In accordance with further aspects of the present invention, the tiller module includes a first tiller module having a first moveable tiller base configured to receive a first tiller that is configured to receive a first steering force and a second tiller module having a second moveable tiller base configured to receive a second tiller that is configured to receive a second steering force. The first tiller module generates a first tiller differential signal and the second tiller module generates a second tiller differential signal. The tiller controller sums the first tiller differential signal and the second tiller differential signal such that the steering signal is generated to direct the steering mechanism to conform with a composite of the first steering force and the second steering force. The steering signal causes both the first moveable tiller base and the second moveable tiller base to move to a feedback position representative of the current position of the steering mechanism.